You and a friend are doing a free fall demonstration where one of you drops a tennis ball from the top of a tall building while the other throws a second tennis ball from the same starting height

Question

The first tennis ball was dropped from a height of 20.0 meters. Assume g=9.81m/s^2

The second tennis ball was thrown down with an initial velocity of -4.00m/s from the same starting height of 20.0 meters

Find the fall time and final velocity of the dropped tennis ball

Find the fall time and final velocity of the thrown tennis ball

Answer 1

For the dropped ball, the time is given by 20=.5gt^2 which gives t = 2.02 s

The velocity is given by v=0-gt and since we know t from before we get v = - 19.8 m/s

For the ball thrown down we need to set up a quadratic using y0 and y

0=20-4t-4.905t^2

4.905T^2+4t-20=0

t=1.65 s

The velocity is now given by v = -4 - 9.81 * 1.65 = -20.2 m/s